This disclosure relates to connecting components of dissimilar materials.
One example of a rocket engine is the RL10 rocket engine manufactured by Pratt & Whitney Rocketdyne, a wholly owned subsidiary of the assignee. Another example of a rocket engine is the J-2X rocket engine also manufactured by Pratt & Whitney Rocketdyne. The three major components of such engines are a turbopump, a combustion chamber and an exhaust nozzle. The exhaust nozzle commonly includes a metallic regeneratively cooled nozzle connected to a non-metallic nozzle extension.
During operation of the rocket engine, the turbopump is used to supply a fuel and an oxidant, such as liquid hydrogen and liquid oxygen respectively, to the combustion chamber. The liquid hydrogen and liquid oxygen are expanded in the combustion chamber and burned to produce hot, pressurized rocket gases. The hot, pressurized gases are flowed at high velocities to the exhaust nozzle. The exhaust nozzle allows further expansion of the gases to increase the velocity of the gases before the gases exit the engine, thereby increasing the thrust of the rocket.
The regeneratively cooled nozzle may be fabricated from thin walled tubes shaped to form the required nozzle contour. Liquid hydrogen fuel is flowed through these tubes to provide convective cooling to the tubes and regenerative heating to the hydrogen fuel. The convective cooling ensures that the temperature of the tubes is consistent with the temperature limits required for structural integrity of the nozzle.
The non-metallic nozzle extension is commonly constructed from materials having low coefficients of thermal expansion, which allows the nozzle extension to operate in the extreme temperatures of rocket engine exhaust gas without being cooled. A common challenge in rocket engine design is connecting the metallic nozzle to the non-metallic nozzle extension. In spite of cooling the metallic nozzle, a significant mismatch in thermal expansion may exist between the metallic nozzle and the non-metallic nozzle extension. The thermal mismatch between nozzle and nozzle extension may act to place stresses on joints between the components, as the metallic nozzle grows radially at operating temperatures while the nozzle extension remains substantially the same size. For example, the expanded metallic nozzle may place bending stresses on bolts connecting the nozzle to the non-metallic nozzle extension.